It's definitely possible, but probably not easy.
It there a case in the game, where after-battle healing is disabled?
Is there a situation or a complex of circumstances where you can't heal after battle for some reason?
If yes, then you can explore the ways to "enable" this for all other battle aswell. If not (or if it doesn't fit well), then you should explore the executable file (post-game menu is a separate binary file) to achieve what you need.
I also like your idea, since it's super-easy to just have some element-levels at the end of the battle for guaranteed healing. Consumables falls off very quickly.
Maybe it can be done easier with element flags. Are all healing elements available in post-battle screen? Is there different flags for in-battle healing and post-battle healing? Probably not, but I don't remember, worth checking.
But executable editing is the best available choice, probably could be done dirty with just 1-2 instructions.
